1. Field of the Invention
The present invention relates to a dust removing device and an image pickup apparatus, and particularly to the removal of foreign matter such as dust adhering to a surface of an optical member provided in an image pickup apparatus such as a digital camera or in an image reading apparatus such as a scanner.
2. Description of the Related Art
In an image pickup apparatus such as a digital camera that picks up an image of an object by receiving an optical image of the object and then converting the optical image into an electrical signal, light that is taken thereinto is received by an image pickup device such as a charge-coupled-device (CCD) sensor or a complementary-metal-oxide-semiconductor (CMOS) sensor. The electrical signal (photoelectric conversion signal) is output from the image pickup device, is converted into image data, and is recorded on a recording medium such as a memory card. In such an image pickup apparatus, an optical low-pass filter or an infrared cut filter is provided on the front side (object side) of the image pickup device.
In such an image pickup apparatus, if any pieces of foreign matter such as dust adheres to the surface of a cover glass of the image pickup device, the optical low-pass filter, or the infrared cut filter, the pieces of foreign matter may appear as black spots in a resultant image. Particularly, in a digital single-lens reflex camera including an interchangeable lens, foreign matter such as dust may be taken into the body of the digital camera from the opening of the lens mount when the lens is interchanged with another. Consequently, such foreign matter may adhere to the surface of the cover glass of the image pickup device or the filter.
In this respect, Japanese Patent No. 4724584 and Japanese Patent Laid-Open No. 2004-12474 each disclose a technology in which dust adhering to the surface of a vibrating member such as a cover glass or a filter are removed by deforming the vibrating member in the thickness direction (by exciting vibrations in an out-of-plane bending vibration mode), utilizing the expansion and contraction of piezoelectric elements.
Japanese Patent No. 4724584 discloses a dust removing device that removes, with vibrations, dust adhering to areas around an optical sensor included in a digital camera or a scanner. The dust removing device includes a vibrating plate (vibrating member). A piezoelectric element is fixed to one of two flat surfaces of the vibrating plate. When a voltage is applied to the piezoelectric element, bending vibrations that displace the vibrating plate in the thickness direction are generated, whereby dust that is present in an area (optically effective area) of the surface of the vibrating plate that influences image formation is removed. The amplitude of vibration is insufficient at positions corresponding to the nodes of vibration. Therefore, a plurality of vibration modes are used in the removal of dust in the optically effective area.
Japanese Patent Laid-Open No. 2004-12474 discloses a configuration in which piezoelectric elements are fixed to the front surface and the back surface, respectively, of a transmissive member (vibrating member) that is provided in an image reading apparatus and allows an image of document to be transmitted therethrough. The transmissive member is vibrated by the piezoelectric elements that are fixed to the two surfaces, whereby dust adhering to the transmissive member is removed. In Japanese Patent Laid-Open No. 2004-12474, the contours of the piezoelectric elements on the front and back surfaces of the transmissive member conform to each other when projected in a direction that is normal to the surfaces of the transmissive member.
The dust removing device disclosed by Japanese Patent No. 4724584 employs a method in which the nodes of vibration are shifted by vibrating the piezoelectric element at a plurality of driving frequencies sequentially. Although the order of vibration (the number of nodes of vibration) is changed, the positional shifts of the nodes are small near the piezoelectric element. Consequently, the amplitude of vibration is insufficient.
In the configuration disclosed by Japanese Patent Laid-Open No. 2004-12474 also, the amplitude of vibration near the piezoelectric elements is considered to be insufficient.